CVE-2025-37953

Description

In the Linux kernel, the following vulnerability has been resolved:sch_htb: make htb_deactivate() idempotentAlan reported a null pointer dereference in htb_next_rb_node()after we made htb_qlen_notify() idempotent.It turns out in the following case it introduced some regression:htb_dequeue_tree(): |-> fq_codel_dequeue() |-> qdisc_tree_reduce_backlog() |-> htb_qlen_notify() |-> htb_deactivate() |-> htb_next_rb_node() |-> htb_deactivate()For htb_next_rb_node(), after calling the 1st htb_deactivate(), theclprio[prio]->ptr could be already set to null, which meanshtb_next_rb_node() is vulnerable here.For htb_deactivate(), although we checked qlen before calling it, incase of qlen==0 after qdisc_tree_reduce_backlog(), we may call it againwhich triggers the warning inside.To fix the issues here, we need to:1) Make htb_deactivate() idempotent, that is, simply return if we already call it before.2) Make htb_next_rb_node() safe against ptr==null.Many thanks to Alan for testing and for the reproducer.

Risk Information

Associated Vulnerability

Patch Details

References

https://nvd.nist.gov/vuln/detail/CVE-2023-1234
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-1234